package network;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    // 启动服务器
    public void start() throws IOException {
        System.out.println("server start!");
        // 1. 读取请求并分析, 此处 requestPacket 是 receive 的输出参数.
        while (true) {
            DatagramPacket requestPacket = new DatagramPacket(new byte[1024],1024);
            socket.receive(requestPacket);
            // 此处把二进制数据, 转成字符串.
            String request = new String(requestPacket.getData(),0,requestPacket.getLength());
            // 2. 根据请求计算响应
            String response = process(request);
            // 3. 最后把响应返回给客户端
            DatagramPacket responsePacket = new DatagramPacket(
                    response.getBytes(),
                    response.length(),
                    requestPacket.getSocketAddress()
            );
            socket.send(responsePacket);
            // 4. 打印日志
            System.out.printf("[%s,%d], request: %s, response: %s\n",
                    requestPacket.getAddress().toString(),
                    requestPacket.getPort(),
                    request,
                    response
                    );
        }
    }

    // 根据请求计算响应
    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server = new UdpEchoServer(9090);
        server.start();
    }

}
